The primary objective of this Phase I dose-escalating study of recombinant human interleukin-12 (rhIL-12) is to assess the safety and maximum tolerated dose of rhIL-12 when administered by subcutaneous injection in patients with cancer. The secondary objectives are to determine the immunopharmacologic profile of rhIL-12; to explore the antitumor efficacy of the dosing schedule and route of administration; and, in selected patients, to evaluate the serum of concentrations of rhIL-12 administered as a subcutaneous injection.